I. Field of the Invention
This invention relates to a method and an apparatus for fluidizing crushed, pulverized, comminuted, powdered or other particulate solids, with or without some added liquid, in a hopper, to enable this material to be extruded through a restrictive aperture or to cause it to conform precisely to the shape of a mold. Thus, the invention relates to such materials in conditions in which, in the absence of fluidizing they cannot flow or can only flow sluggishly under gravity. The invention is primarily concerned with rendering cement, gypsum or plaster mixes sufficiently fluid to be formed by extrusion or molding into predetermined shapes which due to compaction and normal chemical action harden or set sufficiently rapidly for practical purposes without the necessity for adopting additional chemical means, heat treatment or the application of high pressure to the extruded or molded material. The said cement, gypsum or plaster mixes may have granular or fibrous additives such as sand, gravel or crushed rock aggregates, glass, asbestos, particles of steel, polypropylene or other synthetic or natural fibers, also ground rubber and cork. The invention is also applicable to the extrusion in the form of slabs or ribbons of road making materials such as concrete and aggregate mixes or bitumenbound aggregate or asphalt, or plain aggregates or natural soils.
II. Description of the Prior Art
Heretofore compaction of concrete has been effected after the material has been placed in a mold or positioned where it is permanently required. Thus, pressure compaction requires a wet mix which makes relatively weak concrete unless excess water is removed by additional pressure or by a vacuum-suction method. Pressure systems may only be used on static equipment. With road making machines where compaction is effected after the concrete has been laid by the use of vibrators inserted into the concrete, segregation and irregular compaction is a common fault. Compaction by the use of extrusion processes which work by screw or hydraulic pressure cause stress in the material causing it to bow or curve. Normally work is limited to extrusions having fairly large cross-sectional areas, say of 10 cms. by 12.5 cms.